Small Intestinal Bacterial Overgrowth in Critically Ill Patients

Small intestine bacterial overgrowth (SIBO) remains to this day a syndrome that is not fully understood. Initially, it was considered quite rare, but today there are reports suggesting a SIBO prevalence between 6 to 15% of healthy, asymptomatic people and reaching 80% in patients with irritable bowel syndrome. It is often involved in various disorders, such as diarrhea and malabsorption. It is defined as an increase in the number and/or disturbance in the type of bacteria in the upper part of the intestinal tract.

SIBO occurs when the homeostatic mechanisms of the small intestine are disturbed. The two main conditions that favor microbial overgrowth in the small intestine are decreased acid secretion from the stomach and small bowel dyskinesia.

The literature is scarce concerning the effects of SIBO on critically ill patients. To our knowledge this is the first study investigating the effects of SIBO on mechanically ventilated patients. It is a non-invasive observational study employing a modified technique to obtain exhaled air from the ventilator tubes to perform a standard hydrogen breath test for SIBO diagnosis. Lactulose is used as a substrate. Specifically, each patient is administered 20 g of lactulose diluted in 400 ml of water through the nasogastric tube. Measurements are performed at 0-15-30-45-60-90-120-180 min from lactulose administration. During measurements, a valve attached to a collecting bag at the end of the expiratory limb of the breathing circuit, is kept open and the collecting bag is filled by several patient exhalations. After valve closure and bag isolation, the air is drawn by a 50 ml polyethylene syringe which is connected to the valve system to prevent losses and/or contamination. Then the air is blown into the breath hydrogen monitor and the expired hydrogen measurement is recorded.

The hydrogen breath test is repeated at predetermined, protocol-based time intervals for all participants included in the study; 1st/day of admission, 3rd, 5th and 7th day of ICU stay. The 1st day measurement serves as a measure of eligibility, and patients exhibiting abnormal values of hydrogen breath testing at Day 1 are excluded from the study.

An increase by more than 20 ppm of eH2 from baseline within 90 min was considered an abnormal measurement suggesting SIBO. Moreover, an increase by more than 12 ppm of eH2 from baseline within the first 30 minutes followed by a second rise within the next 15 minutes (double peak) was also considered an abnormal measurement suggesting SIBO.

The primary objective of this study is assessment of the prevalence of SIBO on critically ill mechanically ventilated ICU patients. Secondary outcomes include investigation of the effects of SIBO on ventilator associated pneumonia, as well as ICU length of stay and all-cause in-hospital mortality rate in critically ill patients.

Inclusion criteria

• critically ill patients, in need of mechanical ventilation with an expected ICU length of stay and expected mechanical ventilation duration of more than 48 hours

Exclusion criteria

• abnormal hydrogen breath test on the day of ICU admission (Day 1)
• recent (up to four weeks before ICU admission) antimicrobial therapy or patients already receiving antimicrobial therapy on admission
• recent (up to four weeks before ICU admission) use of gastroprotective medication, probiotics and prokinetics
• patients with known gastrointestinal disease prior to admission
• recent abdominal surgery resulting in planned or unplanned ICU admission
• extubation or death before protocol completion (7 days) constitute exclusion criteria after enrollment